1. Formal Concept Analysis: Mathematical Foundations;Ganter,1999
2. Conceptual scaling;Ganter,1989
3. The quotient space theory of problem solving;Zhang;Fundamenta Informatcae,2004
4. Rough set theory based on two universal sets and its applications;Liu;Knowledge-Based Systems,2010
5. K.E. Wolff, A conceptual view of knowledge bases in rough set theory, in: Proceedings of the Second International Conference on Rough Sets and Current Trends in Computing, vol. 7, 2000, pp. 188–192.